Phase Interferometry Depth Camera Calibration
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) for virtual and augmented reality systems face inefficiencies in depth measurement due to structured light and time of flight depth cameras, where structured light inefficiently uses sensor pixels and time of flight cameras struggle with disambiguating optical paths, leading to suboptimal depth determination.
Innovation Solution
A depth camera assembly in the HMD that emits a series of periodic illumination patterns with phase shifts, allowing each pixel to independently determine depth based on captured intensities, optimizing sensor usage and improving depth measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If structured light depth camera projects pattern with different characteristics in different portions, then depth measurement capability is achieved, but sensor pixel utilization efficiency deteriorates (less than 10% of sensor pixels collect light)
Solution Approach 1:
The patent changes the illumination pattern from structured light with spatially varying characteristics to a uniform periodic pattern (sinusoid) that illuminates the entire field of view evenly. This parameter change allows all sensor pixels to collect light simultaneously, achieving 100% pixel utilization while maintaining depth measurement capability through phase shift analysis
Solution Approach 2:
The patent employs periodic illumination patterns (sinusoids) with different phase shifts to encode depth information. By projecting multiple periodic patterns with known phase relationships and analyzing the phase shifts in captured images, the system achieves accurate depth measurement while uniformly utilizing all sensor pixels
2Measurement precision
If time of flight depth camera uses multiple sensor pixels to measure depth, then depth measurement capability is achieved, but computational complexity increases and optical path disambiguation becomes insufficient
Solution Approach 1:
The patent replaces the time-of-flight measurement mechanism with a phase shift analysis mechanism using periodic illumination. Instead of measuring round-trip light travel time, the system encodes depth information in the phase shifts of sinusoidal patterns, which can be extracted through simpler correlation or Fourier analysis, reducing computational complexity
Solution Approach 2:
The patent uses multiple copies of the same periodic illumination pattern with different phase shifts rather than relying on complex optical path analysis. By capturing multiple images with known phase relationships and comparing them, the system determines depth through phase difference calculation, which is computationally more efficient and provides better optical path disambiguation
3Measurement precision
If illumination source and imaging device are displaced by specific distance, then phase interferometry depth measurement is enabled, but device complexity increases
Solution Approach 1:
The patent makes the displacement between illumination source and imaging device serve multiple functions: it creates the phase interferometry effect for depth measurement while also defining the baseline for stereo-like depth calculation. This single structural feature performs dual functions, reducing overall device complexity despite the intentional displacement
Solution Approach 2:
The patent introduces a spatial dimension (displacement between illumination source and imaging device) to enable phase interferometry. This dimensional separation creates the necessary optical path difference for phase measurement while maintaining a relatively simple planar configuration that doesn't significantly increase three-dimensional device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the efficiency and accuracy of depth determination in HMDs by allowing each pixel to determine depth independently, improving the overall performance of virtual and augmented reality systems.
Implementation Method 1
The illumination source is configured to emit a series of periodic illumination patterns (e.g., a sinusoid) into the local area. Each periodic illumination pattern of the series is phase shifted by a different amount.
Implementation Method 2
A depth camera assembly (DCA) is calibrated by determining, for each pixel of a sensor included in an imaging device of the DCA, a calibration offset value that when added to a determined phase shift of a periodic illumination pattern observed by the pixel, results in a calibrated phase shift.
Data Source
AI summary
A depth camera assembly (DCA) determines distances between the DCA and objects in a local area within a field of view of the DCA. The DCA projects a series of sinusoidal patterns into the local area DCA and captures images of the sinusoidal patterns via a sensor. The DCA determines a distance between the DCA and locations in the local area based on a phase shift each of the sinusoidal patterns captured by each pixel of the sensor. Initially, a calibration offset is determined for each pixel of the sensor by emitting the sinusoidal patterns onto a target at a predetermined distance from the DCA and using phase shifts for a pixel and the predetermined distance to determine the pixel's calibration offset.